In natural environments, and particularly in aquatic environments, certain microorganisms preferentially exist in sessile, colony-forming cells which form a biofilm. A biofilm is a conglomerate of microbial organisms embedded in a highly hydrated matrix of exopolymers, typically polysaccharides, and other macromolecules (Costerton 1981). Biofilms may contain either single or multiple microbial species and readily adhere to such diverse surfaces as river rocks, soil, pipelines, teeth, mucous membranes, and medical implants (Costerton, 1987). By some estimates biofilm-associated cells outnumber planktonic cells of the same species by a ratio of 1000-10,000:1 in some environments.
Prevention of colonization by and eradication of biofilm-associated microorganisms is an important, and often difficult, problem in medicine. Unlike planktonic organisms, which are relatively susceptible to biocides, e.g, antibiotics, the structural matrix established during biofilm formation can make the colonizing cells able to withstand normal treatment doses of a biocide. It is known that when organisms are isolated from biofilms and then grown in planktonic culture, they lose many of the characteristics associated with the progenitor cells, in particular, the ability to produce a glycocalyx (Costeron, 1987). In the biofilm, the glycocalyx matrix appears to serve as a barrier which protects and isolates the microorganisms from host defense mechanisms such as antibodies and phagocytes as well as from antimicrobial agents including surfactants, biocides and antibiotics (Costerton, 1981). In one study, biofilm-associated bacteria were able to survive a concentration of antibiotic 20 times the concentration effective to eliminate the same species of bacteria grown in planktonic culture (Nickel, 1985a). The higher doses of biocides needed to eliminate biofilm growth may not well tolerated in the body.
Biofilm infections can occur in a variety of disease conditions. In some tissue infections, such as prostatitis, the infective bacterium is capable of growing in the infected tissue in both biofilm (sessile) and circulating (planktonic) form (Costerton, 1987). Although growth of the planktonic cells can be controlled by antibiotic treatment, the biofilm itself may be refractory to treatment, providing, in effect, a reservoir of infection which can lead to recurrence of the infection after antibiotic treatment.
Osteomyelitis is another biofilm-associated bacterial infection which can be difficult to treat. In severe cases, the infected bone must be exposed operatively, and the interior of the bone scraped to remove infected regions. The bone is then packed with a matrix material which serves as a carrier for an antibiotic. Even with this extreme treatment, the biofilm infection may not be completely destroyed, and further such treatment may be necessary (Gristina, 1984).
Biofilm infection is also associated with septic arthritis, where biofilm formation on joint surfaces can lead to a chronic and recurrent infection In addition to sepsis, the biofilm infection can cause destruction of the joint surface material (Gristina).
Biofilm formation can also be a serious complication in bio implants, such as bone prostheses, heart valves, pacemakers and the like. Biofilm formation on exposed surfaces of a bio implant can degrade the function of the implant (Passerini), as in the case of implanted valves, lead to serious joint or bone infections, as in the case of a bone prosthesis (Gristina), and in all cases, provide a source of difficult-to-treat septic infection (Jacques).